{"id":44008,"date":"2025-12-15T10:01:43","date_gmt":"2025-12-15T15:01:43","guid":{"rendered":"https:\/\/stateofthenation.info\/?p=44008"},"modified":"2025-12-15T10:41:56","modified_gmt":"2025-12-15T15:41:56","slug":"unprecedented-3i-atlas-still-shows-an-anti-tail-before-closest-approach-of-3i-atlas-to-earth","status":"publish","type":"post","link":"https:\/\/stateofthenation.info\/?p=44008","title":{"rendered":"

UNPRECEDENTED — 3I\/ATLAS Still Shows an Anti-Tail Before Closest Approach Of 3I\/ATLAS To Earth<\/b><\/h2>"},"content":{"rendered":"

Avi Loeb<\/p>\n

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An image of 3I\/ATLAS, taken on December 13, 2025 at 21:30:26 UTC with a 0.26-meter telescope in Rayong, Thailand. The field of view spans 0.72 million kilometers on a side at the distance of 3I\/ATLAS from Earth, 271 million kilometers. The bottom three panels show the projected brightness map in false colors and black & white, respectively. The top panel shows a rotational-gradient brightness map with a Larson-Sekanina filter. A prominent anti-tail, uncommon for comets, points in the direction of the Sun towards the lower left. (Image Credit:\u00a0Teerasak Thaluang<\/a>)<\/figcaption><\/figure>\n

As of today, December 14, 2025, the interstellar object\u00a03I\/ATLAS<\/a>\u00a0is at a distance of about 270.5 million kilometers from Earth. Its images are delayed by a quarter of an hour, as it takes light from 3I\/ATLAS 15 minutes to reach us. On December 19, 2025, 3I\/ATLAS will get closest to Earth at a perigee distance of 268.9097 (+\/-0.0060) million kilometers.<\/p>\n

The latest image of 3I\/ATLAS was taken by Teerasak Thaluang on December 13, 2025 at 21:30:26 UTC with a 0.26-meter telescope in Rayong, Thailand (as reported\u00a0here<\/a>). The rotational-gradient brightness map shows a prominent anti-tail, uncommon for comets, pointing in the direction of the Sun.<\/p>\n

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Whereas an anti-tail had been seen for solar system comets as a temporary perspective effect when the Earth crossed the comets\u2019 orbital plane, this is clearly not the case with 3I\/ATLAS. The anti-tail was apparent in the first Hubble Space Telescope image, taken on July 21, 2025, when 3I\/ATLAS was approaching the Sun from a geocentric distance of 2.98 times the Earth-Sun separation (AU) \u2014 as reported\u00a0here<\/a>\u00a0and analyzed\u00a0here<\/a>, and was also apparent in the second Hubble image taken on November 30, 2025, when 3I\/ATLAS was receding away from the Sun at a distance of 1.91 AU from Earth \u2014 as reported\u00a0here<\/a>. The anti-tail was also apparent in thousands of images taken in between these dates.<\/p>\n

The anti-tail of 3I\/ATLAS is therefore not a perspective effect. It is a real physical jet, with a glow extending from 3I\/ATLAS towards the Sun. Its nature is a mystery because gas and micrometer-dust particles are expected to be pushed away from the Sun by solar radiation pressure and the solar wind, creating the appearance of a tail \u2014 as routinely seen in solar-system comets. There was no mention of this mystery at the NASA press conference about 3I\/ATLAS on November 19, 2025 (accessible\u00a0here<\/a>).<\/p>\n

To explain the physics of the anti-tail of 3I\/ATLAS, I have written three scientific papers. The first two of these peer-reviewed papers, co-authored with Eric Keto (accessible\u00a0here<\/a>\u00a0and\u00a0here<\/a>), associate the anti-tail with scattering of sunlight by fragments of ice shed from the sun-facing side of 3I\/ATLAS. These tiny ice particles evaporate before they get pushed back significantly by the solar radiation pressure and so they never appear as a conventional cometary tail. The third (single-authored) paper, published on December 8, 2025\u00a0here<\/a>, associates the anti-tail with a swarm of objects that lag behind 3I\/ATLAS because of its non-gravitational acceleration away from the Sun (as reported by JPL Horizons\u00a0here<\/a>). Analysis of the latest Hubble image could potentially favor one of these explanations.<\/p>\n

By recognizing anomalies, we can learn something new. By ignoring them, we remain ignorant.<\/mark><\/p>\n

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